A display device driven by so-called an active matrix manner has come into practical use, and the production amount is increasing. To carry out the active matrix driving, a liquid crystal display panel or an organic EL panel is driven with a Thin Film Transistor (hereinafter referred to as a TFT), which is made of an amorphous Si (hereinafter referred to as an a-Si) or a polycrystalline Si (hereinafter referred to as a Poly-Si), and is formed on the glass substrate as a switching element of the pixel.
Particularly, with the use of Poly-Si which has high carrier mobility and allows high-speed operation, recent technologies have succeeded to integrate even the peripheral drivers etc. onto a glass substrate. Such a structure has been manufactured as a product.
However, in such a display device, like a liquid crystal display device or an OLED (Organic Light Emitting Diode: organic EL) using a large glass substrate, there is some problems in using a driver IC including a transistor made of a non-singlecrystalline Si, particularly a poly-Si, because of the variation in characteristics due to the particular crystal grain boundaries of poly-Si and poor quality of gate insulating film, thereby disabling the transistor to be adopted for integration of a complex system. In this view, and also considering display quality (uniformity), a device with higher performance and less characteristic variation is required.
Particularly, when a highly-integrated semiconductor device is directly mounted to a display substrate, or on systematization thereof, there are difficulties to ensure high-speed performance and high integration density because of insufficiencies in driving speed, micro fabrication, and device performance (mobility, control of the threshold, sharpness of transmission characteristic). The foregoing structure is therefore insufficient in device performance and integration density to realize a desired system integration in a driving system used for an image processor or a timing controller, which requires a superior-performance.
Accordingly, there is a serious difficulty in fabrication of pixel TFTs and a high-performance/high-density driver for driving the pixel TFTs directly onto a large display substrate, of a glass or the like.
To overcome this problem, there is a technology of mounting (assembling) a singlecrystalline Si driver LSI (Large Scale Integrated circuit) using a COG (Chip On Glass), in which an LSI, formed from a singlecrystalline Si, is assembled onto a display substrate through, for example, flip-chip bonding with an anisotropic conductive film etc.
Since a general LSI includes MOS (Metal Oxide Semiconductor) transistors formed from bulk singlecrystalline Si, the individual transistor needs to be driven separately to ensure adequate operation. Therefore, to separate the transistors into individual pieces (device isolation), or to prevent latch-up by a parasitic bipolar transistor, ion implantation, such as channel stop implantation section 101 or multiple well 102, is performed as shown in FIG. 13. However, the trend of miniaturization of transistor arises a new problem regarding the area for device isolation. Thus, to reduce the area for device isolation, retrograde well (reverse-impurity concentration gradient-well) structure or the like has been introduced; however, this structure requires ion implantation many times and makes the process complicated, thus causing a cost rise and a decrease in yield. Further, requirement of processes for forming bumps etc. increases time for fabrication, thereby decreasing the yield.
Further, in manufacturing a liquid crystal display device or an OLED display device, there are some restrictions, for example, the driver IC needs to be assembled onto a completed panel. This arises various problems, such as less-flexible and complicated manufacturing, low efficiency in distribution and manufacturing, and a cost rise which causes a decrease in yield.
This problem can be solved by device transfer. In the device transfer, a device made of a singlecrystalline Si is formed on a bulk Si substrate, and is bonded to a glass substrate to create a display panel, and the insulator is then separated from the device layer through some kind of exfoliation. Note that, this structure in which a device of a singlecrystalline Si is formed on an insulator is called a SOI (Silicon On Insulator).
A possible method of performing the device transfer is removing an oxide film under the singlecrystalline Si from the SOI structure by etching so as to create a thin film device (Kopin Co. Ltd.) This method are described in detail, for example in Japanese Laid-Open Patent Application Tokuhyohei 07-503557 (published on Apr. 13, 1995), and the following Documents 1 and 2.    Document 1: J. P. Salerno “Single Crystal Silicon AMLCDs”, Conference Record of the 1994 International Display Research Conference (IDRC) p. 39-44(1994)    Document 2: Q.-Y. Tong & U. Gesele, SEMICONDUCTOR WAFER BONDING: SCIENCE AND TECHNOLOGY_, John Wiley & Sons, New York (1999)
Tokuhyohei 07-503557 discloses a method of manufacturing a display panel for an active matrix-type liquid crystal display device, using a semiconductor device on which a singlecrystalline Si thin film transistor is transferred, the transfer is formed on a glass substrate in advance with an adhesive.
Further, other prior arts of the present invention can be found in Japanese Laid-Open Patent Application Tokukaihei 10-125880 (published on May 15, 1998), and the following Documents 3 and 4.    Document 3: K. Warner, et. al., 2002 IEEE International SOI Conference: October, pp. 123-125 (2002)    Document 4: L. P. Allen, et. al., 2002 IEEE International SOI Conference: October, pp. 192-193 (2002)
Tokukaihei 10-125880 discloses a method of first creating level differences in the singlecrystalline Si, forming a small polishing stopper whose polishing rate is smaller than the singlecrystalline Si, then transferring the Si onto another Si substrate, and polishing the divided surface. By thus forming the stopper in a concave section of the step and using the difference in polishing speed, this method makes an island-shaped singlecrystalline Si thin film.
However, the conventional semiconductor substrates, and semiconductor devices, and fabrication methods for those have the following disadvantages.
First, in a SOI structure, since the devices are formed on a silicon wafer, the total size of all devices to be provided thereon needs to fall within the silicon (Si) wafer. The size of silicon (Si) wafer is limited, and may be smaller than a large glass substrate in some cases.
Further, since a singlecrystalline Si device formed on the silicon (Si) wafer is bonded onto a glass substrate with an adhesive of, for example, an epoxy resin, there are certain difficulties to additionally performing a defect recovery thermal process (Annealing process), an inter-layer insulating film forming process, or a metal-wiring forming process after the bonding. Therefore, there is a serious difficulty in connecting between the device formed in advance on a large glass substrate, and a singlecrystalline Si device transferred onto the glass substrate through mutual wiring.
Further, this method is more complicated as it first forms an operation region on a solid phase epitaxial film, which is a singlecrystalline layer of a thin film grown on a silicon dioxide (SiO2), to make a singlecrystalline Si device, and then the silicon dioxide (SiO2) is divided by etching. Therefore, this method suffers from a decrease in yield (transfer process, division/retention of thin film, epitaxial growth).